Conventionally, a composite structure is widely known, which is defined by tightening a countersunk hole component having a countersunk hole and a screw hole component having a screw hole by a plate screw component. In this art, a male thread of the plate screw component is engaged with a female thread of the screw hole component, such that a seat part of the plate screw component having a taper surface shape is seated on the countersunk hole of the countersunk hole component shaped in the taper surface shape. Thus, the countersunk hole component and the screw hole component are connected with each other. Accordingly, it becomes possible to downsize the composite structure in the axial direction of the plate screw component.
Patent Literature 1 discloses a valve timing adjustment device as an example in which such a technology is applied. In the valve timing adjustment device disclosed in Patent Literature 1, an outer rotor rotating with a crankshaft is configured by a composite structure, in which an inner rotor rotating with a camshaft is relatively rotated inside the outer rotor.